Controlled impedances of printed circuits

Impedance is measured in ohms and makes it possible to measure the quality of copper tracks. The impedance is an alternating current (AC) characteristic that increases with frequency and becomes critical for printed circuits operating at frequencies above 200 or 300 Mhz.

Impedance calculator software is a good starting point to determine the track width (w) and insulation thickness (h) of a given impedance.

In terms of signal traffic in printed circuits, when the tracks carry signals at high frequencies, great care must be taken in designing the tracks to match the impedance of the upstream and downstream components. The longer the route or the higher the frequency, the better adaptation is required.

When producing the printed circuit with controlled impedance, the impedance will be controlled by acting on the dimensions of the tracks and the distance between them, i.e. the insulation.

For a multilayer printed circuit with a specific stack-up, it must be taken into account that the internal tracks with controlled impedance are shielded by copper planes and for this reason only the thickness of the insulation between layers and tracks and the track thickness must be taken into account.